System and method for delivery of a vapor phase product to a point of use

ABSTRACT

Provided are a novel system and method for delivery of a vapor phase product to a point of use, as well as a novel on-site chemical distribution system and method. The system for delivery of a vapor phase product includes a storage vessel containing a liquid chemical under its own vapor pressure, a column connected to receive the chemical in liquified state from the storage vessel, wherein the chemical is fractionated into a contaminated liquid heavy fraction and a purified light vapor fraction and a conduit connected to the column for removing the purified light vapor fraction therefrom. The system is connected to the point of use for introducing the purified vapor fraction thereto. Particular applicability is found in semiconductor manufacturing in the delivery of electronics specialty gases to one or more semiconductor processing tools.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and a method for delivery of avapor phase product to a point of use. The present invention alsorelates to an on-site chemical distribution system and to a method foron-site distribution of a chemical. The invention has particularapplicability in the delivery of electronics specialty gases used in themanufacture of semiconductor devices to one or more semiconductorprocessing tools.

2. Description of the Related Art

In the semiconductor manufacturing industry, different chemicals aresupplied to processing tools in gaseous form for carrying out a varietyof semiconductor fabrication processes. Examples of such processesinclude diffusion, chemical vapor deposition (CVD), etching, sputteringand ion implantation. These chemicals are conventionally referred to aselectronics specialty gases (ESG's).

Many of the chemicals employed in the above processes, while introducedto the processing tools in the gaseous state, are stored as liquidsunder their own respective vapor pressures. Typically, the liquidchemicals have room temperature vapor pressures greater than atmosphericpressure.

These chemicals are conventionally stored in gas cylinders which arehoused within gas cabinets. A typical volume of such a gas cylinder isless than about 50 liters. A partial list of chemicals stored in thismanner, the pressures under which they are stored and their criticalpressures are provided below in Table 1:

                  TABLE 1                                                         ______________________________________                                                                Vapor                                                                         Pressure                                                                      of Gas at                                                                              Critical                                                             20° C.                                                                          Pressure                                     Chemical     Formula    (psia)   (psia)                                       ______________________________________                                        Ammonia      NH.sub.3   129      1636                                         Boron Trichloride                                                                          Bcl.sub.3  19       1071                                         Carbon Dioxide                                                                             CO.sub.2   845      1118                                         Chlorine     Cl.sub.2   100      634.7                                        Chlorotrifluoride                                                                          ClF.sub.3  26.1     837.4                                        Dichlorosilane                                                                             SiH.sub.2 Cl.sub.2                                                                       24       746.6                                        Disilane     Si.sub.2 H.sub.6                                                                         48       956.9                                        Hydrogen Bromide                                                                           HBr        335      1240                                         Hydrogen Chloride                                                                          HCl        628      1198                                         Hydrogen Fluoride                                                                          HF         16       940.2                                        Nitrous Oxide                                                                              N.sub.2 O  760      1050                                         Perfluoropropane                                                                           C.sub.3 F.sub.8                                                                          115      388.5                                        Sulfur       SF.sub.6   335      545.0                                        Hexafluoride                                                                  Tungsten     WF.sub.6   16       619.1                                        Hexafluoride                                                                  ______________________________________                                    

A single gas cabinet typically supplies the chemical vapor to a singleor at most several semiconductor processing tools. Operation of the gascabinets and the cylinders housed therein can be a hazardous, laborintensive and costly activity. As the chemical is depleted, it isimperative that the gas cylinder be replaced with careful and properhandling procedures.

In order to reduce the total number of gas cabinets required in thesemiconductor manufacturing facility, it has recently been proposed thata single gas cabinet service multiple processing tools. Since thevolumes of the cylinders housed in the gas cabinets does not increasewith the number of processing tools being serviced, replacementfrequency of the cylinders in the cabinets necessarily increases. It is,however, desirable to minimize the frequency of cylinder replacement,not only for safety concerns but also to reduce the risk of introducingimpurities that may cause significant product loss.

In addition to increasing the frequency of gas cylinder replacement, theinstantaneous flowrate of the gas being withdrawn from each cylinderincreases with the additional processing tools serviced by a given gascabinet. Such an increase in flowrate can lead to the presence ofentrained liquid droplets in the gas stream, which can result inflowrate fluctuations, accelerated corrosion and premature failure offlow control components in the gas distribution system. Furthermore, thecorrosion products can lead to contamination of the highly pure processgases. This contamination can have deleterious effects on the processesbeing run, and ultimately on the manufactured semiconductor devices.

To meet the requirements of the semiconductor processing industry and toovercome the disadvantages of the related art, it is an object of thepresent invention to provide novel systems for delivery of a chemicalstored as a liquid under its own vapor pressure. The systems makepossible the simultaneous servicing of multiple processing tools andadditionally can perform a purification function, whereby highly puregases useful in semiconductor manufacture can be produced. Because ofsuch purification function, the systems make possible the use of arelatively low purity starting material, which material would otherwisenot be useful, for example, in semiconductor manufacturing.

According to one aspect of the invention, entrained liquid droplets inthe gas obtained from the liquid chemical can be minimized oreliminated. As a result, single phase process gas flow can be obtained,in contrast to known systems and methods.

It is a further object of the present invention to provide novel methodsfor delivery of a chemical stored as a liquid under its own vaporpressure, which methods can be practiced on the inventive systems.

It is a further object of the present invention to provide a novelon-site chemical distribution system, and a method for on-site chemicaldistribution which method can be practiced on the system.

Other objects and aspects of the present invention will become apparentto one of ordinary skill in the art upon review of the specification,drawings and claims appended hereto.

SUMMARY OF THE INVENTION

The foregoing objectives are met by the systems and methods of thepresent invention. According to a first aspect of the present invention,a novel system for delivery of a vapor phase product to a point of useis provided. A storage vessel contains a liquid chemical under its ownvapor pressure. A column is connected to receive the chemical inliquified state from the storage vessel, wherein the chemical isfractionated into a contaminated liquid heavy fraction and a purifiedlight vapor fraction. A conduit is connected to the column for removingthe purified light vapor fraction therefrom, wherein the system isconnected to the point of use for introducing the purified vaporfraction thereto.

According to a second aspect of the invention, a system for delivery ofa vapor phase product is provided which involves a plurality of columns.The system comprises a storage vessel containing a liquid chemical underits own vapor pressure, and a plurality of columns. Each columnfractionates a liquid introduced therein into a respective heavy liquidfraction and a respective light vapor fraction. A first column of theplurality of columns is connected to receive, as the liquid introducedtherein, the chemical in liquified state from the storage vessel. Aconduit is connected to a second column of the plurality of columns forremoving therefrom the respective light vapor fraction. The system isconnected to the point of use for introducing the second column lightvapor fraction thereto.

A method for delivery of a vapor phase product to a point of use is alsoprovided. According to the method, a storage vessel containing a liquidchemical under its own vapor pressure is provided. A stream of thechemical is introduced in liquified state into a column, whereby thechemical is fractionated into a contaminated liquid heavy fraction and apurified light vapor fraction. The purified light vapor fraction isintroduced to the point of use.

According to a further aspect of the invention, a method for delivery ofa vapor phase product to a point of use is provided. A storage vesselcontaining a liquid chemical under its own vapor pressure is provided. Aplurality of columns are provided. Each column fractionates a liquidintroduced therein into a respective heavy liquid fraction and arespective light vapor fraction. A first column of the plurality ofcolumns is connected to receive, as the liquid introduced therein, thechemical in liquified state from the storage vessel. The respectivelight vapor fraction is removed from a second column of the plurality ofcolumns, and the second column light vapor fraction is introduced to thepoint of use.

According to a further aspect of the invention, an on-site chemicaldistribution system is provided. The system comprises a storage vesselcontaining a liquid chemical under its own vapor pressure and aplurality of vapor supply systems. The vapor supply systems areconnected in parallel and downstream from the storage vessel, and areconnected to receive the chemical in liquified state. Each of the vaporsupply systems produces a respective purified vapor product, and isconnected to one or more respective points of use for introducing therespective purified vapor product thereto.

In accordance with yet another aspect of the invention, a method foron-site distribution of a chemical is provided, which method can bepracticed on the above-described system. The method comprises providinga storage vessel containing a liquid chemical under its own vaporpressure, and introducing the chemical in liquified form to a pluralityof vapor supply systems. The vapor supply systems are connected inparallel and downstream from the storage vessel. Each of the vaporsupply systems produces a respective purified vapor product. Therespective purified vapor products are introduced to one or morerespective points of use.

The systems and methods have particular applicability in the delivery ofan electronics specialty gas to one or more points of use in asemiconductor manufacturing facility, for example to one or moresemiconductor processing tools.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become apparent fromthe following detailed description of the preferred embodiments thereofin connection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a system for delivery of a vapor phaseproduct in accordance with one aspect of the invention; and

FIG. 2 is a schematic diagram of a system for delivery of a vapor phaseproduct in accordance with a further aspect of the invention; and

FIG. 3 is a schematic diagram of on-site chemical distribution system inaccordance with a further aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present invention provides an effective way to provide a high puritychemical which is stored as a liquid under its own vapor pressure to oneor more points of use, for example, processing tools used in thefabrication of semiconductor devices.

As used herein, the term "a liquid chemical under its own vaporpressure" means a chemical, which at ambient conditions would be in thegas phase, has had its temperature and/or pressure modified such that itis in its liquid state at or near (i.e., within about +5° C. of) itsboiling point.

With reference to FIG. 1, a preferred embodiment of the inventive systemand method will be described.

The system includes a storage vessel 1 which contains a chemical storedas a liquid under its own vapor pressure. The liquid chemical can begenerated on-site and stored in a bulk storage vessel or, moretypically, the liquid chemical is delivered to the use site via bulktransport vessel, for example, a tube trailer. Storage vessel 1preferably has an internal volume of greater than about 100 liters,preferably from about 200 to 60,000 liters. Sizing of the components andthe flowrates involved are not to be limited, but depend on the specificapplication involved.

The specific liquid chemical contained in storage vessel 1 is dependenton, for example, on the processing tools being serviced and theprocesses being run therein. In semiconductor manufacturing processes,typical liquid chemicals include those electronics specialty gases(ESG's) specified in Table 1 above, i.e., ammonia (NH₃), borontrichloride (BCl₃), carbon dioxide (CO₂), chlorine (Cl₂),chlorotrifluoride (ClF₃) dichlorosilane (SiH₂ Cl₂), disilane (Si₂ H₆),hydrogen bromide (HBr), hydrogen chloride (HCl), hydrogen fluoride (HF),nitrous oxide (N₂ O),perfluoropropane (C₃ F₈), sulfur hexafluoride(SF₆), trichlorosilane (SiHCl₃, and tungsten hexafluoride (WF₆).Additional ESG's include, for example, the class of materials known asperfluorocarbons (PFC's).

For electronics manufacturing applications, it is desirable that storagevessel 1 be compatible with the liquid chemical contained therein andwith the high purities required in the manufacturing process. Thestorage vessel is preferably constructed of stainless steel and can besurface treated, for example, by mechanical polishing orelectropolishing and passivation.

The liquid chemical contained in the storage vessel is preferably ofhigh purity. However, because of the purification function of the systemand method, the liquid chemical purity can be relatively low comparedwith conventional practice.

Storage vessel 1 is connected to a conduit 2 for transferring thechemical in liquified form from the storage vessel to other componentsof the system. Suitable materials of construction for liquidtransferring conduit 2 and other conduits which contact the chemical inliquified form generally include but are not limited to, 316 stainlesssteel. The specific material selected, however, will depend upon thespecific liquid chemical being used.

Flowrates throughout the system will depend on the specific applicationsinvolved, and the system is preferably designed around the flowraterequirements.

A high purity block, bleed and purge system 3 can be disposed downstreamof the point of connection of storage vessel 1 to conduit 2. The purposeof the block, bleed and purge system 3 is to ensure that contaminantsare not introduced into the system during replacement of storage vessel1.

In the exemplified embodiment, block, bleed and purge system 3 includesa high purity inert purge gas source 4, such as nitrogen, argon orhelium, for the removal of ambient contaminants and for the removal ofresidual chemicals in the system during replacement of storage vessel 1.Preferably, a nitrogen-driven venturi purge system is employed for thispurpose. A purge gas line 5 is connected to conduit 2 downstream of thepoint of connection of storage vessel 1. The purge gas is typically bledoff through a bleed line 6, which can be connected to a waste treatmentunit 7 for further processing.

Depending upon the specific chemical employed, waste treatment unit 7can comprise, for example, a unit for adsorption, scrubbing, thermaldecomposition, storage or a combination thereof. To reduce the quantityof liquid chemical and/or contaminated purge gas that is sent to wastetreatment unit 7, it is desirable to minimize the volume of block, bleedand purge system 3.

Control of the gas flow in block, bleed and purge system 3 can beaccomplished by manipulation of valves V1 and V2 in conduit 2, valve V3in purge gas line 5 and valve V4 in bleed line 6. The system can befurther integrated with a cycling valve, so that removal of ambientcontaminants or residual chemical can be accomplished through a seriesof pressure-vacuum cycles.

Flow control throughout the system, including operation of block, bleedand purge system 3, can be automated with a controller 8. Suitablecontrol means are known in the art, and include, for example, one ormore programmable logic controllers (PLCs) or microprocessors.

After connection of storage vessel 1 to the system and purging, theliquid chemical can be transported through the system from the storagevessel, in liquified form, into a column 9, which is in fluidcommunication with the storage vessel. The liquid chemical is introducedinto the column at an intermediate point thereof.

Flow of the chemical into the column can be aided by use of a pump 10,such as a positive displacement pump. The inlet of the pump ispreferably connected as closely as possible to the purge block tominimize pressure losses on the suction side. The outlet of pump 10 isconnected to a conduit 11 through which the liquid chemical istransported to column 9. Depending on the nature of the impurities to beremoved and the degree of purification desired, it may be desirable toemploy a plurality of columns where multiple. Where multiple columns areused, they may be disposed in series or in parallel. Multiple columnsystems are further described below in reference to FIG. 2.

Various types of columns are envisioned for use with the invention. Thecolumn should allow intimate contact between liquid and vapor phases,whereby a purified vapor can be obtained therefrom. Suitable columnsinclude, for example, distillation, absorption and adsorption columns,and chemical conversion/reaction units of the trace impurity orimpurities. Where multiple columns are employed, the columns can be ofthe same or a different type.

The column typically contains one or more liquid-vapor phase contactpromoting devices, such as structured, ordered and random packingmaterials, or sieve, bubble-cap, valve, Kittel plate, flexitray, showertrays and other special tray designs, to provide for a high degree ofcontact between the liquid and vapor phases in the column. Of theseliquid-vapor phase contact promoting devices, randomly packed column andbubble-cap are preferred.

Suitable packing materials are known in the art, and include, forexample, Rachig rings, Lessing Rings, Berl saddles, spiral partitionrings and grid packing. Suitable materials of construction for thepacking materials include, for example, glass, quartz, ceramics andstainless steel. Choice of the packing type and material of constructionis dependent on factors, such as the chemical being purified and itsmass flow rate.

Where an adsorbent is to be employed in the column, the adsorbent willdepend on the particular chemical being treated, as well as the impurityor impurities to be removed. Typical adsorbents include, for example,ascerite for CO₂ removal from N₂ O, metal impregnated carbons for sulfurcompound removal from CO₂, activated carbons for removal of volatilehydrocarbons, and molecular sieves, alumina and silica based products.

Where trays are employed in the purification column, the trays aretypically constructed of stainless steel. The total number of trays willdepend on the specific chemical being treated and the nature andconcentration of impurities therein, as well as the degree ofpurification desired.

Liquid feed to column 9 can be controlled by use of a controller 8. Thecontroller description set forth above applies also to the liquid feedcontroller, and to each of the controllers to be described below. Thus,while FIG. 1 illustrates a single controller for controlling variousaspects of the system, the use of multiple controllers is alsoenvisioned.

The controller can operate, for example, based on input from a levelsensor/transmitter 24 which monitors the liquid chemical level at thebottom of column 9. The controller can turn on and off pump 10 asrequired to maintain the liquid chemical level at the bottom of thecolumn at a desired, predetermined level.

While the pressure and temperature maintained in the column will varydepending on the specific liquid chemical being treated and the natureof the impurities therein, column 9 preferably operates at a pressure offrom about 1 to 100 bar, more preferably from about 5 to 20 bar, and ata temperature of from about -200 to 300° C., more preferably from about-40 to 150° C.

The liquid chemical introduced into the column is fractionated into acontaminated liquid heavy fraction, and a light vapor fraction. As usedherein, the term "heavy fraction" refers to a stream removed from aportion of a column below the liquid feed stage. The heavy product is ina liquid state, and is preferably removed from the bottom of the column.

Also as used herein, the term "light vapor fraction" refers to a streamremoved from a portion of a column above a feed stage. The light vaporproduct is preferably removed from the top of the column.

At least a portion of the contaminated liquid heavy fraction isconverted into a saturated vapor in reboiler/vaporizer 12. The saturatedvapor is returned to column 9 through a conduit 13, connected to thecolumn at a point below conduit 11. In this way, the saturated vapor andthe liquid chemical introduced into column 9 can contact each otherintimately in a countercurrent manner. A high purity vapor thereby canbe produced. Conduit 18 is connected to the column at a point aboveconduit 11, preferably at the top of the column, for removing the highpurity vapor therefrom. The high purity vapor stream has a puritycompatible with semiconductor manufacturing processing, preferably inthe ppm or sub-ppm range.

The heat duty Q_(in) for vaporizer 12 can be provided by a heat source,such as an electric heater for direct heat input or a heating mediumstream, for example, water, glycol solution, halocarbon fluids, or otherheat transfer fluids which are known to those skilled in the art.

Residual contaminated liquid in the vaporizer can be periodicallydrained therefrom through vaporizer purge line 14. Such purging can helpto minimize the concentration of the heavier, i.e., high boiling,components in the saturated vapor. The removed contaminated liquid canbe introduced into a holding vessel 15, which can be periodicallydrained using pump 16. This waste material can be sent to a wastetreatment unit and/or can be pumped into a container for shipment backto the chemical supplier for purification and reuse.

Various aspects of the operation of vaporizer 12, such as the heat dutyQ_(in) required to vaporize a major portion of the liquid feed can becontrolled by a controller 8 based on the total system pressure. Thetotal system pressure can be measured by any known means, such aspressure sensor 17 in conduit 18. The controller can additionally beused to control purging of the contaminated liquid from the vaporizer ona predetermined schedule.

In order to remove or minimize any entrained liquid droplets present inthe high purity vapor withdrawn from the column through conduit 18 andto prevent the formation of such droplets due to condensation, the highpurity vapor can be superheated. Such superheating can ensure singlephase gas flow. This superheating can be achieved by use of one or moresuperheaters 19, with the pressure of the high purity vapor upstream ofthe superheater being controlled by a pressure regulator 20.

The superheater can be any unit which effectively removes the entrainedliquid droplets from the gas stream. For example, a heat exchanger(e.g., a shell-and-tube type heat exchanger) using a suitable heattransfer fluid, for example, halocarbons such as freons (e.g., freon22), can be used for this purpose. Other examples of suitable structuresfor superheating the gas include a resistance-type heater, heatergrid-type packing material, heated sintered or porous structures, andany other direct or indirect methods of heating.

The temperature of the vapor passing through the superheater ismonitored at its outlet by temperature monitor 21. To prevent theformation of condensate caused by expansion and cooling of the gas as itpasses through pressure regulator 22 and the subsequent gas distributionpiping, the heat duty Q_(in) supplied to the high purity vapor can beregulated by controller 8.

An additional feature of the invention is a surge tank 23. Surge tank 23acts as a reservoir for the high purity vapor, and minimizes pressurefluctuations in the gas delivered to the point(s) of use. As shown inthe exemplified embodiment, the superheater and surge tank arepreferably provided in combination as a single unit. The superheater canalternatively be disposed in series with the surge tank.

The pressure in the surge tank, or combination surge tank/superheater,is preferably maintained at only several psi, for example, from 1 to 30psi, above the normal distribution piping system pressure, butsignificantly lower, for example, from 20 to 50 psi, than thepurification column pressure.

To allow servicing of the one or more points of use, gas distributionpiping is connected thereto. Thus, in the case of semiconductormanufacturing, one or more semiconductor processing tools can beconnected to receive the high purity vapor.

FIG. 2 illustrates a further aspect of the present invention, wherein aplurality of columns are employed. By employing a plurality of columns,higher levels of purity for the gas phase product may be obtained thanfor the single column system and method, especially if both light andheavy impurities exist in the feed chemical. The description set forthabove with respect to FIG. 1 is applicable to the plural column system,with various differences being outlined below.

First column 25 is disposed between pump 10 and second column 9, whichcorresponds to the column described in reference to FIG. 1. The chemicalcontained in storage vessel 1 is introduced into first column 25 inliquified form at a feed stage at an intermediate point in the column.The types of columns described above with reference to FIG. 1 areapplicable to column 25.

The liquid feed into first column 25 is fractionated into a liquid heavyfraction and a light vapor fraction. The light vapor fraction is removedfrom first column 25 through conduit 26 disposed above the feed stage,preferably at the top of the column. The light vapor fraction isintroduced into condenser 27, and is at least partially condensedtherein.

A portion of the condensate is reintroduced into column 25 throughconduit 28 as reflux, which is connected to the column at a point abovethe feed stage. The remainder of the light vapor fraction is removedfrom the system through conduit 29. The waste vapor can optionally befurther processed, for example, by a waste treatment facility.

The cooling duty Q_(out) for condenser 27 of first column 25 is providedby a refrigeration cycle which includes refrigeration unit 30 and acooling medium transported to and from the condenser through lines 31and 32, respectively. The operational pressure and temperature of firstcolumn 25 are such that conventional refrigerants can be used as thecooling medium. Suitable refrigerants are known to those skilled in theart, and include, for example, freons such as from 11, 12, 21, 22, 113,114, 115, 134b, 142b, 152a and 216.

The cooling duty for the condenser can be provided by an openrefrigeration cycle, which may use a different cooling medium, such asliquified or gaseous N₂, O₂ or Ar, liquid CO₂ or water.

The liquid heavy fraction is removed from first column 25 throughconduit 33. At least a portion of the removed liquid heavy fraction isintroduced into a reboiler 34. At least a portion thereof is vaporizedand reintroduced in vapor form into first column 25 at a point below thefeed stage through conduit 35. The heat duty Q_(in) for reboiler 34 canbe provided by a heat source, such as an electric heater for direct heatinput or a heating medium stream, for example, water, a glycol solutionor a halocarbon fluid. Other suitable heat transfer fluids are known tothose skilled in the art.

That portion of the liquid heavy fraction which is not introduced intothe reboiler is introduced into second column 9 in liquified form usingpump 10 (described above). As another option, if the operationalpressure difference between first column 25 and second column 9 issufficient to allow flow, pump 10 may be replaced by a control valve forflow control. The remaining components of the system and method stepsare as described above with reference to FIG. 1.

Operation of the condenser and/or the reboiler can be controlled by useof a single or multiple controllers, such as described above. As shownin the exemplified embodiment, controller 8 controls the heat duty toreboiler 34.

For the exemplary two-column system, first column 25 preferably operatesat a pressure in the range of from about 1 to 100 bar, more preferablyfrom about 5 to 20 bar, and at a temperature in the range of from about-200 to 300° C., more preferably from about -40 to 150° C.

The second column 9 preferably operates at a pressure in the range offrom about 1 to 100 bar, more preferably from about 5 to 20 bar, and ata temperature in the range of from about -200 to 300° C., and morepreferably from about -40 to 150° C. These conditions are, of course,dependent on the specific gas being treated and the nature of theimpurities contained therein.

The use of multiple columns is not limited in any way by the illustratedpreferred embodiment. In this regard, more than two columns can beemployed in the present invention, and the columns can be linked in avariety of ways depending, for example, on the chemical being treatedand the nature of impurities. Furthermore, the multiple columns can bedisposed in series and/or in parallel.

A variation of the above-described system and method as applied to asystem and a method for on-site chemical distribution will now bedescribed with reference to FIG. 3.

As in the above-described systems and methods, the on-site distributionsystem and method begin with a storage vessel 1 which contains thechemical stored as a liquid under its own vapor pressure. The storagevessel is connected to a conduit 2 for transferring the chemical inliquified form from the storage vessel to the other components of thesystem. A high purity block, bleed and purge system 3 can be disposeddownstream of the point of connection of storage vessel 1 to conduit 2to prevent contamination of the system.

The pressure of the liquid chemical in conduit 2 can be measured andregulated by pressure sensor P and regulator 36, respectively, thecontrol of which can be automated by use of a controller. In theexemplary embodiment, the liquid chemical is introduced into a liquidreservoir 37, from which it is drawn and delivered to the remainder ofthe system. The internal volume of the liquid reservoir will depend onfactors such as the liquid chemical flow requirements of the system.Suitable materials of construction for the liquid reservoir are the sameas those set forth with respect to storage vessel 1.

It is desirable to eliminate or at least to minimize the formation ofgas in the liquid reservoir. Such gas typically forms as a result of thepressure drop which occurs whenever the chemical is drawn off from theliquid reservoir. The elimination of this gas is particularly desirableprior to introduction of the liquid into a pumping system to preventcavitation.

To minimize gas formation, it is desirable to control the level of theliquid chemical in the reservoir to a value greater than somepredetermined minimum value. This control can be accomplished, forexample, by detecting the liquid level in the reservoir with a levelsensor connected to a controller 38. Based on the measured level,additional liquid chemical can be introduced into the reservoir fromstorage vessel 1 as needed. In addition, an exhaust conduit 38 can beprovided for removing the gas from the liquid reservoir by operation ofcontrol valve V5. The gas removed through exhaust conduit 38 can befurther treated, for example, by a waste treatment facility. The abovedescribed operations can be automated by use of, for example, controller38 alone, or with one or more additional controllers.

From liquid reservoir 37, the liquid chemical is distributed throughoutthe remainder of the system by use of one or more pumps 10", such as apositive displacement pump. For example, a single pump 10" downstreamfrom the storage vessel can be used to transport the liquid chemical toeach of the vapor supply systems 38, as illustrated. As anotherpossibility, each vapor supply system can have one or more dedicatedpumps for transport of the liquid chemical thereto.

The liquid chemical is introduced from pump 10" into main conduit 42,and then via conduits 39 to a plurality of vapor supply systems 38,disposed in parallel with one another. To control flow to each of thevapor supply systems, a respective shut-off valve S and a controllertherefor can be provided. The vapor supply systems each produce apurified vapor stream which is directed to one or more points of use 40.In the exemplified embodiment, the vapor supply systems supply anelectronics specialty gas to one or more semiconductor processing tools.

The details of the vapor supply systems are provided above withreference to FIGS. 1 and 2. In this regard, the vapor supply systemsinclude those components disposed downstream of the pump 10 in FIG. 1and 10' in FIG. 2, leading up to the point of use.

According to a preferred aspect of the invention, an excess of theliquid chemical is introduced into conduit 41, such that the liquid feedto the vapor supply systems does not run out. Main conduit 42 preferablyincludes a recycle leg to return back to liquid reservoir 39 thatportion of the liquid chemical which is not introduced into the vaporsupply systems.

To control back-pressure in conduit, a pressure monitor P and controlvalve V6 are preferably provided in the recycle leg of the conduit. Thecontrol valve can be operated with a controller based on the pressurevalue measured by the pressure monitor. By controlling back-pressure,supply of the requisite amount of liquid chemical to the vapor supplysystems can be ensured.

Because of the difference in density between the liquid and gas phasechemical, it is possible to use piping for transporting the liquidchemical which is of significantly smaller diameter than that used fortransportation of the chemical in its gaseous state. Thus, less space isrequired for the liquid chemical distribution piping than if thechemical were transported entirely in the gas phase. Such liquid phasetransport also helps to reduce pressure fluctuations when compared withgas phase distribution.

As a result of each of the systems and methods described above,characteristics of the gas being delivered can be maintained throughwide fluctuations in flow rate. Such variations can result from thesystem's feeding numerous points of use which have flow raterequirements independent of each other. Fluctuations in theinstantaneous flow rate requirement of greater than about one thousandtimes the average flow rate may be present without adversely affectingthe performance of the systems and methods.

Furthermore, the performance characteristics of the systems and methodsdescribed above can be maintained throughout the campaign of thechemical storage vessel irrespective of the amount of liquid presenttherein. It is preferred, however, that the storage vessel be replacedwhen the chemical volume amounting to about 1 to 20% of the total volumeof the vessel (depending on the specific chemical) remains.

Additionally, a wide array of use patterns is possible with the presentinvention. For example, the invention is compatible with continuous andintermittent operations. This allows flexibility in process design andcan maximize the overall effectiveness of the equipment.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

What is claimed is:
 1. A system for delivery of a vapor phase product toa point of use, the system comprising:a storage vessel containing aliquid chemical under its own vapor pressure; a column connected toreceive the chemical in liquified state from the storage vessel, whereinthe chemical is fractionated into a contaminated liquid heavy fractionand a purified light vapor fraction; and a conduit connected to thecolumn for removing the purified light vapor fraction therefrom; whereinthe system is connected to the point of use for introducing the purifiedvapor fraction thereto.
 2. The system according to claim 1, wherein thestorage vessel is a bulk transport vessel.
 3. The system according toclaim 1, further comprising a block, bleed and purge system disposedbetween the storage vessel and the column.
 4. The system according toclaim 1, wherein the column contains an adsorbent, a packing material,trays or a combination thereof.
 5. The system according to claim 1,further comprising a vaporizer connected to receive at least a portionof the contaminated liquid heavy fraction from the column, the vaporizercomprising a purge line for draining the contaminated liquid heavyfraction therefrom.
 6. The system according to claim 5, furthercomprising a waste treatment unit connected to receive the contaminatedliquid heavy fraction drained through the vaporizer purge line.
 7. Thesystem according to claim 1, further comprising a superheater forsuperheating the purified light vapor fraction.
 8. The system accordingto claim 7, further comprising a surge tank for containing the purifiedlight vapor fraction, wherein the superheater and the surge tank form anintegral unit or separate units.
 9. The system according to claim 8,wherein the superheater and the surge tank form an integral unit. 10.The system according to claim 1, wherein the electronics specialty gasis selected from the group consisting of ammonia (NH₃), borontrichloride (BCl₃), carbon dioxide (CO₂), chlorine (Cl₂), chlorinetrifluoride (ClF₃), dichlorosilane (SiH₂ Cl₂), trichlorosilane (SiHCl₃),disilane (Si₂ H₆), hydrogen bromide (HBr), hydrogen chloride (HCl),hydrogen fluoride (HF), nitrous oxide (N₂ O) ,perfluoropropane (C₃ F₈),sulfur hexafluoride (SF₆), tungsten hexafluoride (WF₆) and aperfluorocarbon.
 11. The system according to claim 1, wherein the pointof use comprises a semiconductor processing tool.
 12. The systemaccording to claim 1, wherein the system is connected to a plurality ofpoints of use.
 13. A system for delivery of a vapor phase product to apoint of use, the system comprising:a storage vessel containing a liquidchemical under its own vapor pressure; and a plurality of columns, eachcolumn fractionating a liquid introduced therein into a respective heavyliquid fraction and a respective light vapor fraction; a first column ofthe plurality of columns being connected to receive, as the liquidintroduced therein, the chemical in liquified state from the storagevessel; and a conduit connected to a second column of the plurality ofcolumns for removing therefrom the respective light vapor fraction;wherein the system is connected to the point of use for introducing thesecond column light vapor fraction thereto.
 14. The system according toclaim 13, wherein the plurality of columns further comprises, in seriesand between the first and second columns, one or more additionalcolumns, the additional columns being connected to receive a respectivelight vapor fraction from a respective preceding column.
 15. The systemaccording to claim 14, wherein the second column is connected to receivethe respective heavy liquid fraction from the preceding column.
 16. Thesystem according to claim 13, wherein the storage vessel is a bulktransport vessel.
 17. The system according to claim 13, wherein thecolumn contains an adsorbent, a packing material, trays or a combinationthereof.
 18. The system according to claim 13, further comprising asuperheater for superheating the second column light vapor fraction. 19.The system according to claim 18, further comprising a surge tank forcontaining the second column light vapor fraction, wherein thesuperheater and the surge tank form an integral unit or separate units.20. The system according to claim 19, wherein the superheater and thesurge tank form an integral unit.
 21. The system according to claim 13,wherein the electronics specialty gas is selected from the groupconsisting of ammonia (NH₃), boron trichloride (BCl₃), carbon dioxide(CO₂), chlorine (Cl₂), chlorine trifluoride (ClF₃) , dichlorosilane(SiH₂ Cl₂), trichlorosilane (SiHCl₃), disilane (Si₂ H₆), hydrogenbromide (HBr), hydrogen chloride (HCl), hydrogen fluoride (HF), nitrousoxide (N₂ O), perfluoropropane (C₃ F₈), sulfur hexafluoride (SF₆),tungsten hexafluoride (WF₆) and a perfluorocarbon.
 22. The systemaccording to claim 13, wherein the point of use comprises asemiconductor processing tool.
 23. The system according to claim 13,wherein the system is connected to a plurality of points of use.
 24. Amethod for delivery of a vapor phase product to a point of use, themethod comprising:providing a storage vessel containing a liquidchemical under its own vapor pressure; introducing a stream of thechemical in liquified state into a column, whereby the chemical isfractionated into a contaminated liquid heavy fraction and a purifiedlight vapor fraction; and introducing the purified light vapor fractionto the point of use.
 25. The method according to claim 24, wherein thestorage vessel is a bulk transport vessel.
 26. The method according toclaim 24, further comprising a step of superheating the purified lightvapor fraction prior to the introducing to the point of use.
 27. Themethod according to claim 26, further comprising containing the purifiedlight vapor fraction in a surge tank prior to the introducing to thepoint of use.
 28. The method according to claim 27, wherein theelectronics specialty gas is selected from the group consisting ofammonia (NH₃), boron trichloride (BCl₃) carbon dioxide (CO₂), chlorine(Cl₂), chlorine trifluoride (ClF₃), dichlorosilane (SiH₂ Cl₂),trichlorosilane (SiHCl₃), disilane (Si₂ H₆), hydrogen bromide (HBr),hydrogen chloride (HCl), hydrogen fluoride (HF), nitrous oxide (N₂ O),perfluoropropane (C₃ F₈), sulfur hexafluoride (SF₆), tungstenhexafluoride (WF₆) and a perfluorocarbon.
 29. The method according toclaim 24, wherein the point of use comprises a semiconductor processingtool.
 30. The method according to claim 24, wherein the purified lightvapor fraction is introduced to a plurality of points of use.
 31. Themethod according to claim 24, wherein the column is operated at apressure of from about 1 to 100 bar, and at a temperature of from about-200 to 300° C.
 32. A method for delivery of a vapor phase product to apoint of use, the method comprising:providing a storage vesselcontaining a liquid chemical under its own vapor pressure; providing aplurality of columns, each column fractionating a liquid introducedtherein into a respective heavy liquid fraction and a respective lightvapor fraction, a first column of the plurality of columns beingconnected to receive, as the liquid introduced therein, the chemical inliquified state from the storage vessel; and removing from a secondcolumn of the plurality of columns the respective light vapor fraction;introducing the second column light vapor fraction to the point of use.33. The method according to claim 32, wherein the storage vessel is abulk transport vessel.
 34. The method according to claim 32, furthercomprising a step of superheating the purified light vapor fractionprior to the introducing to the point of use.
 35. The method accordingto claim 34, further comprising containing the light vapor fraction fromthe final column in a surge tank prior to the introducing to the pointof use.
 36. The method according to claim 32, wherein the electronicsspecialty gas is selected from the group consisting of ammonia (NH₃),boron trichloride (BCl₃), carbon dioxide (CO₂), chlorine (Cl₂), chlorinetrifluoride (ClF₃), dichlorosilane (SiH₂ Cl₂), trichlorosilane (SiHCl₃),disilane (Si₂ H₆), hydrogen bromide (HBr), hydrogen chloride (HCl),hydrogen fluoride (HF), nitrous oxide (N₂ O), perfluoropropane (C₃ F₈),sulfur hexafluoride (SF₆), tungsten hexafluoride (WF₆) and aperfluorocarbon.
 37. The method according to claim 32, wherein the pointof use comprises a semiconductor processing tool.
 38. The methodaccording to claim 32, wherein the purified light vapor fraction isintroduced to a plurality of points of use.
 39. The method according toclaim 32, wherein the plurality of columns operate at a pressure of fromabout 1 to 100 bar, and at a temperature of from about -200 to 300° C.40. A system for delivery of an electronics specialty gas to asemiconductor processing tool, the system comprising:a storage vesselcontaining a liquid chemical under its own vapor pressure; a columnconnected to receive the chemical in liquified state from the storagevessel, whereby the chemical is fractionated into a contaminated liquidheavy fraction and a purified light vapor fraction; and a conduitconnected to the column for removing the purified light vapor fractiontherefrom; wherein the system is connected to the semiconductorprocessing tool for introducing the purified light vapor fractionthereto, and the purified light vapor fraction is an electronicsspecialty gas.
 41. A system for delivery of an electronics specialty gasto a semiconductor processing tool, the system comprising:a storagevessel containing a liquid chemical under its own vapor pressure; aplurality of columns, each column fractionating a liquid introducedtherein into a respective heavy liquid fraction and a respective lightvapor fraction; a first column of the plurality of columns beingconnected to receive, as the liquid introduced therein, the chemical inliquified state from the storage vessel; and a conduit connected to asecond column of the plurality of columns for removing therefrom therespective light vapor fraction; wherein the system is connected to asemiconductor processing tool for introducing the second column lightvapor fraction thereto, and the purified light vapor fraction is anelectronics specialty gas.
 42. A method for delivery of an electronicsspecialty gas to a semiconductor processing tool, the methodcomprising:providing a storage vessel containing a liquid chemical underits own vapor pressure; introducing a stream of the chemical inliquified state into a column, whereby the chemical is fractionated intoa contaminated liquid heavy fraction and a purified light vaporfraction; and introducing the purified light vapor fraction to thesemiconductor processing tool, wherein the purified light vapor fractionis an electronics specialty gas.
 43. A method for delivery of anelectronics specialty gas to a semiconductor processing tool, the methodcomprising:providing a storage vessel containing a liquid chemical underits own vapor pressure; providing a plurality of columns, each columnfractionating a liquid introduced therein into a respective heavy liquidfraction and a respective light vapor fraction, a first column of theplurality of columns being connected to receive, as the liquidintroduced therein, the chemical in liquified state from the storagevessel; and removing from a second column of the plurality of columnsthe respective light vapor fraction; introducing the purified lightvapor fraction to the semiconductor processing tool, wherein thepurified light vapor fraction is an electronics specialty gas.
 44. Anon-site chemical distribution system, comprising:a storage vesselcontaining a liquid chemical under its own vapor pressure; and aplurality of vapor supply systems connected in parallel and downstreamfrom the storage vessel, the vapor supply systems being connected toreceive the chemical in liquified state and each producing a respectivepurified vapor product; wherein the vapor supply systems are eachconnected to one or more respective points of use for introducing therespective purified vapor product thereto.
 45. The on-site chemicaldistribution system according to claim 44, wherein each of the vaporsupply systems comprises one or more columns.
 46. The on-site chemicaldistribution system according to claim 45, wherein the one or morecolumns contain an adsorbent, a packing material, trays or a combinationthereof.
 47. The on-site chemical distribution system according to claim45, wherein each of the vapor supply systems further comprises asuperheater for superheating the purified light vapor fraction.
 48. Theon-site chemical distribution system according to claim 44, wherein theone or more points of use comprise one or more semiconductor processingtools.
 49. The on-site chemical distribution system according to claim44, further comprising a reservoir for containing the liquid chemical,the reservoir being disposed downstream of the storage vessel andupstream of the vapor supply systems.
 50. The on-site chemicaldistribution system according to claim 49, further comprising a recycleline connected to the reservoir for recycling thereto that portion ofthe liquid chemical which is not fed to the plurality of vapor supplysystems.
 51. A method for on-site distribution of a chemical, the methodcomprising:providing a storage vessel containing a liquid chemical underits own vapor pressure; introducing the chemical in liquified form to aplurality of vapor supply systems connected in parallel and downstreamfrom the storage vessel, each of the vapor supply systems producing arespective purified vapor product; and introducing the respectivepurified vapor product to one or more respective points of use.
 52. Themethod according to claim 51, wherein each of the vapor supply systemscomprises one or more columns.
 53. The method according to claim 52,wherein the one or more columns contain an adsorbent, a packingmaterial, trays or a combination thereof.
 54. The method according toclaim 51, further comprising superheating the purified vapor productsprior to introduction to the one or more points of use.
 55. The methodaccording to claim 51, wherein the one or more points of use compriseone or more semiconductor processing tools.
 56. The method according toclaim 51, further comprising recycling to a reservoir that portion ofthe liquid chemical which is not fed to the plurality of vapor supplysystems.
 57. The method according to claim 51, wherein the high purityvapor phase product is an electronics specialty gas.
 58. The systemaccording to claim 57, wherein the electronics specialty gas is selectedfrom the group consisting of ammonia (NH₃), boron trichloride (BCl₃),carbon dioxide (CO₂), chlorine (Cl₂), chlorine trifluoride (ClF₃),dichlorosilane (SiH₂ Cl₂), trichlorosilane (SiHCl₃), disilane (Si₂ H₆),hydrogen bromide (HBr), hydrogen chloride (HCl), hydrogen fluoride (HF),nitrous oxide (N₂ O),perfluoropropane (C₃ F₈), sulfur hexafluoride(SF₆), tungsten hexafluoride (WF₆) and a perfluorocarbon.